1. Field of the Invention
This invention relates to the field of suspensions for disk drives. More particularly, this invention relates to the field of a hard disk drive (HDD), dual stage actuation (DSA) suspension having a PZT encapsulation dam formed in the suspension.
2. Description of Related Art
Magnetic hard disk drives and other types of spinning media drives such as optical disk drives are well known. FIG. 1 is an oblique view of an exemplary prior art hard disk drive and suspension for which the present invention is applicable. The prior art disk drive unit 100 includes a spinning magnetic disk 101 containing a pattern of magnetic ones and zeroes on it that constitutes the data stored on the disk drive. The magnetic disk is driven by a drive motor (not shown). Disk drive unit 100 further includes a disk drive suspension 105 to which a magnetic head slider (not shown) is mounted proximate a distal end of load beam 107. Suspension 105 is coupled to an actuator arm 103, which in turn is coupled to a voice coil motor 112 that moves the suspension 105 arcuately in order to position the head slider over the correct data track on data disk 101. The head slider is carried on a gimbal which allows the slider to pitch and roll so that it follows the proper data track on the disk, allowing for such variations as vibrations of the disk, inertial events such as bumping, and irregularities in the disk's surface.
Both single stage actuated disk drive suspensions and dual stage actuated (DSA) suspension are known. In a single stage actuated suspension, only voice coil motor 112 moves suspension 105. In DSA suspensions, in addition to voice coil motor 112 which moves the entire suspension, at least one microactuator is located on the suspension in order to effect fine movements of the magnetic head slider to keep it properly aligned over the data track on the spinning disk. The microactuator(s) provide much finer control and much higher bandwidth of the servo control loop than does the voice coil motor alone, which effects relatively coarse movements of the suspension and hence the magnetic head slider.
FIG. 2 is a top plan view of suspension 105, which is a representative prior art DSA suspension, and FIG. 3 is a close-up view thereof in the area around microactuators 14. Two piezoelectric lead zirconate titanate (PZT) microactuators 14 are affixed to suspension 105 on microactuator mounting shelves 18 that are formed within base plate 12, such that the PZTs span respective gaps in base plate 12. Microactuators 14 are affixed to mounting shelves 18 by non-conductive epoxy 16 at each end of the microactuators. The positive and negative electrical connections can be made from the PZTs to the suspension's flexible wiring trace and/or to the grounded base plate by a variety of techniques including those disclosed in commonly owned U.S. Pat. No. 7,751,153 to Kulangara et al., U.S. Patent Publication 2010/0177445 by Fuchino, and U.S. Patent Publication No. US 2009/00886379 by Hanya et al. An exemplary electrical connection 22 is shown in FIG. 3. The electrical connections to the PZT are a matter of design choice according to known techniques, and will not be shown or described further herein. Other examples of DSA suspensions are given in U.S. Pat. No. 6,661,619 to Nishida et al., and U.S. Pat. No. 6,594,104 to Tokuyama et al.
FIG. 4 is an oblique view of the area around the microactuators in another prior art suspension 305. This suspension is similar to the suspension of FIG. 3 and includes a serpentine spring 130 that helps the suspension return to its nominal state when the PZTs are not energized.
In the prior art, microactuators on HDD suspensions have often been placed on the base plate or other base portion of the suspension. Probably less common are DSA suspensions in which the microactuator is placed on the load beam itself, including close to the head slider or even underneath the head slider. The microactuators in DSA suspensions are often, although not exclusively, piezoelectric devices such as lead zirconate titanate (PZT) crystals. The PZT microactuators normally take the form of relatively thin wafers having a square or rectangular shape when viewed from the top.
One drawback suffered by DSA suspensions having PZT microactuators is that, in operation, the PZT crystals can shed small particles especially from the sides. These small particles can contaminate the disk drive assembly causing scratches on the surface of the spinning disk platter when the particles come between the magnetic head slider and the surface of the disk on which the data is stored.
One solution previously proposed is to encapsulate the sides of the PZT using epoxy or similar material. An example of such a solution is presented in U.S. Pat. No. 6,393,681 to Summers, which is assigned to the assignee of the present application.